ON AN UNSEASONABLY hot and humid day, Zach Jones, 19, is brought to your ED after becoming dizzy and very weak 22 miles into his first marathon. He's alert and oriented and says he has muscle aches. The paramedics have started 100% oxygen via nonrebreather mask and an I.V. infusion of 0.9% sodium chloride solution running wide open. They report that Mr. Jones's blood glucose was 86 mg/dL by finger-stick test (normal range, 60 to 110 mg/dL), and that he vomited on the way to the hospital. You notify the ED physician and take Mr. Jones's vital signs, which are: BP, 120/70 mm Hg ...